'Extreme Weight Loss' Contestant Suffers Major Heart Attack Scare

We're with the cast of Extreme Weight Loss after 400-pound David collapsed during a workout, triggering fears that he had suffered a massive heart attack at just 30 years old.

"When you start to look at the dizziness, the nausea, the vomiting and especially the heart palpitations, that was the final straw," said trainer Chris Powell. "I said, 'You know what? It's not worth it.'"

David's weight elevated to dangerous levels after he lost his brother and his sister within weeks of each other, Powell told us. David's brother passed away after an accidental gun shooting, while his sister later lost her life to a seizure when David forgot to administer her medication.

"After both those accidents, I just hated myself," said David. "I couldn't believe that I was still alive and they were dead. I felt responsible for their death."

Today, David has made a huge physical transformation. So much so that Powell assured us, "The kind of shape David's in now, I can promise you he's not going to have a heart attack any time in the near future."